1998 Ford F-150 Starting problems

On my 98 f150 I drove about 3 miles down the road to a friends house and cut the vehicle off. When I went to crank the truck up all I got was a clicking noise from the selanoid on the passenger side firewall. I checked the battery and tried jumping the truck off with no luck. Several people told me it was the starter. I took off the starter and had it checked was told it was bad. Bought a new starter put it on and got the same thing, just clicking. I took it back and was told the starter was bad. Bought a new starter that did work fine and put it on. When I went to crank the truck I got the same thing, just clicking and I think it is shorting out the starter everytime I try to turn it over. Also when I turn the key to start it is showing no oil pressure yet all the other gauges are showing good. Is this a short in the wiring or could it be something more serious?